Separately, both printed office wastepaper and plastic coated paperboard have been difficult to deink. Office waste including non-impact (laser and xerox) toners is not easily purified by conventional deinking methods such as washing, flotation and dispersion. Alternatively, agglomeration deinking methods are used but are expensive procedures due to the high chemical cost of the agglomeration chemicals used.
Recovery of paper fiber from milk cartons and other types of liquid packaging or plastic coated or laminated paper or paperboard is hampered by plastic contamination in the recovered pulp. Slotted screens can be used to remove plastic particles but are not entirely effective. The liquid packaging often contains a wet strength additive, which prevents effective repulping, and the resulting flakes of unpulped paperboard tend to seal over and plug the screen plates. Also, liquid packaging tends to contain a significant percentage of long softwood fibers, which also make screening with fine slots more difficult. The thin flexible plastic also tends to plug fine slots, forcing the use of larger slots which compromise the screening efficiency. Therefore, removal of plastic contaminants resulting from laminated plastic or plastic coatings remains a problem.
Conventional recycling processes utilize well characterized and presorted grades of wastepaper. Mixed wastepaper streams are not readily recycled because of their non uniform properties and changing chemical compositions of the constituents.
Separate processes for deinking various types of printed paper and plastic coated paperboard are known in the art. Representative of such processes include: U.S. Pat. No. 1,628,931 to Todd which discloses a process for extracting wax from waste waxed paper by dissolving in a solution of tri-sodium phosphate and soda ash; U.S. Pat. No. 2,776,209 to O'Flynn which discloses a method for deinking and dewaxing wastepaper by repulping in a non-acidic aqueous solution of urea; U.S. Pat. No. 3,933,577 to Penque which discloses a method for recycling municipal solid waste (garbage) by shredding waste material and passing through an air elutriator to separate into a heavy stream containing metals and a light stream containing paper, plastics, etc.; and U.S. Pat. No. 4,332,638 to Mauer which provides a process and apparatus for sorting long and short fibers from a mixture of different types of wastepaper, including plastic coated paper.
The prior art describes separate methods for deinking printed wastepaper and plastic coated paperboard. However, the art has not shown a deinking process for recycling a combined mixture of printed wastepaper and plastic coated paperboard to produce clean pulp. The invention is directed to the provision of such a process in which simultaneous repulping of a mixture of plastic coated and printed paper and contact with a deinking chemical presents a synergy in which separated plastic components attract and effectively adsorb ink agglomerates to form ink/plastic clusters. These clusters are readily removed from the pulp medium to produce a high level of pulp cleanliness for creating recycled paper products. Further advantages of the invention over prior practices include repulping both long fibered paperboard pulp with short fibered office waste paper together which makes the removal steps easier, particularly the screening stages, and prevents the screens from becoming overloaded with plastic and flakes of unpulped paperboard. It further allows the use of fine slotted screens for complete removal of plastic from the pulp.
There is a need in the art for processes which are less complex to produce recycled paper. This invention is directed to the provision of such processes which have wide range applications in creating recycled paper with a high level of cleanliness, and using a low dosage of agglomeration chemical.
Accordingly, it is a broad object of the invention to provide a deinking process for the recycling of plastic coated and printed paper.
Another object of the invention is to provide a low cost deinking process that effectively and efficiently removes ink and plastic particles without using high concentrations of expensive agglomeration chemicals.
A still further object of the invention is to provide a recycled paper product having improved strength and a high level of cleanliness made from recycled plastic containing paper and printed wastepaper.